Why do you want to 'protect the lens' Shawn? Are you going to film in dusty, wet, smokey, children places? If not, don't use a 'protective filter' as you'll add to the flare, reduce the hooding and have two more surfaces that you have to keep spotless (on top of the front element).

A high-quality filter will make very little difference to the quality of the image and will protect the front lens element from life's little dings. Furthermore, the very act of having a protective filter on the front keeps the front of the lens (and the back of the filter) clean.

I keep a B+W filter on the front of all my cameras (still and video). The coating on the filter is just as if not more resistant to flare and other problems as the coating on the lens.

Of course one always needs to operate with a lens hood and other spot shade tools to keep the light out of the lens.

Obviously one will have a hard time placing any sort of cover over a fish-eye.

BTW, you do know that a fish-eye adapter will grossly distort the image? For most viewers, a fish-eye image is very difficult to visually decipher.

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Mike Rehmus
Hey, I can see the carrot at the end of the tunnel!